eval.cpp

parser in C++~~~~~~~~~~~~

/**
 * \file eval.cpp
 *
 * A dummy implementation for example purposes.  Just barely enough is
 * implemented to allow the parser to run.  Merely returns the input
 * expression without evaluating it.
 */

#include "eval.hpp"
#include "math.h"


/**
   * \brief Show different error message
   */
void errorfct(int i = 0) 
{ 
     
    if (i == 1) 
        cerr<< "ERROR: missing operand"<< endl; 
    else if (i == 2) 
        cerr<< "ERROR: missing operator"<< endl; 
    else if (i == 3) 
        cerr<< "ERROR: too many operands or too few operands"<< endl; 
    else if (i == 4) 
        cerr<< "ERROR: wrong type of operand"<< endl; 
    else if (i == 5) 
        cerr<< "ERROR: not an operator"<< endl; 
    else cerr<< "ERROR"<< endl; 
    exit(1); 
} 
 
 
/** 
   * \brief Do evaluation for different operator, "ceiling", "if" and "+" 
   * 
   * \param count    to count the number of operand 
   * \param operand        to point the first operand or the result after recursion 
   * \param operand2    to point the second operand 
   * \param operand3    to point the third operand 
   * \param cur        to point the cdr of c 
   * \param result    to store the result after calculation 
   * \param checkint    to check if the result is an integer 
   * 
   * \return the operand after evaluation 
   */ 
 
Cell* eval(Cell* const c) 
{ 
    int count = 0; 
     
    // for empty list 
    if (nullp(c)) 
        errorfct(2); 
     
    // for input single operand, i.e 8 
    if (!listp(c)) 
        return c; 
     
    // for no function or no operator 
    if (nullp(car(c))) 
        errorfct(2); 
     
    // for wrong operator 
    if (!symbolp(car(c))) 
        errorfct(5); 
 
    // for operator "ceiling" 
    if (get_symbol(car(c))=="ceiling") 
    { 
        if (nullp(cdr(c)))    //check whether operand exist 
            errorfct(1); 
        if (nullp(car(cdr(c))))    //check whether operand exist 
            errorfct(2);    //check whether operand exist 
 
        Cell *operand = car(cdr(c));    // first operand 
        Cell *cur = cdr(c); 
 
        while (cur != NULL)    // count the number of operand 
        { 
            count++; 
            cur = cdr(cur); 
        } 
 
        if (count != 1)    // check whether the number of operand is suitable 
            errorfct(3); 
        else if (listp(operand))    //the operand is a function list 
        { 
            Cell *temp = eval(operand);    //recursion 
            if (!doublep(temp))    //check whether the type of operand is suitable 
                errorfct(4); 
 
            Cell *result = make_int(ceil(get_double(temp)));    //ceiling the operand 
            return result; 
        } 
        else if (!listp(operand))    //the operand not a function list 
        { 
            if (!doublep(operand))    //check whether the type of operand is suitable 
                errorfct(4); 
 
            Cell *result = make_int(ceil(get_double(operand)));    //ceiling the operand 
            return result; 
        } 
    } 
 
    // for operator "if" 
    if (get_symbol(car(c)) == "if") 
    { 
        if (nullp(cdr(c)))    //check whether operand exist 
            errorfct(1); 
        if (nullp(car(cdr(c))))    //check whether operand exist 
            errorfct(2); 
     
        Cell *cur = cdr(c); 
     
        while (cur != NULL)    // count the number of operand 
        { 
            count++; 
            cur = cdr(cur); 
        } 
     
        if (count < 2 || count > 3)    // check whether the number of operand is suitable 
            errorfct(3); 
         
        cur = cdr(c); 
        Cell *operand = car(cur);    // first operand 
         
        if (listp(operand))    //the operand is a function list 
            operand = eval(operand); 
     
        if (doublep(operand) && get_double(operand) == 0.0) // check wheather the first operand is zero 
        { 
            if (count != 3)    // check whether the number of operand is suitable 
                errorfct(3); 
            else  
            { 
                Cell *operand3 = car(cdr(cdr(cur)));    //third operand 
                if (listp(operand3)) 
                    operand3 = eval(operand3); 
                return operand3; 
            } 
        } 
        else if (intp(operand) && get_int(operand) == 0) // check wheather the first operand is zero 
        { 
            if (count != 3)    // check whether the number of operand is suitable 
                errorfct(3); 
            else 
            {    Cell *operand3 = car(cdr(cdr(cur)));    //third operand 
                if (listp(operand3)) 
                    operand3 = eval(operand3); 
                return operand3; 
            } 
        } 
        else 
        { 
            Cell *operand2 = car(cdr(cur));    // second operand 
            if (listp(operand2)) 
                operand2 = eval(operand2); 
            return operand2; 
        } 
    } 
 
    // for operator "+" 
    if (get_symbol(car(c)) == "+") 
    { 
        if (nullp(cdr(c)))    //check whether operand exist and initialize it 
            return make_int(0); 
        if (nullp(car(cdr(c))))    //check whether operand exist 
            errorfct(2);     
     
        Cell *operand = car(cdr(c));    // first operand 
        Cell *cur = cdr(c);     
        double result = 0.0;    // initialize the result 
        int checkint = 0;    // check the result either double or integer 
         
        while (true) 
        { 
            if (listp(operand))    //the operand is a function list 
                operand = eval(operand);    //recursion 
            if (symbolp(operand))    //check whether the type of operand is suitable 
                errorfct(4); 
            if (intp(operand))    //check the type and calculate 
                result += get_int(operand); 
            else if (doublep(operand)) 
            { 
                checkint = 1; 
                result += get_double(operand); 
            } 
            if (cdr(cur) == NULL) 
                break; 
     
            cur = cdr(cur); 
            operand = car(cur); 
        } 
     
        if (checkint != 0) 
            return make_double(result); 
        else return make_int(result); 
    } 
    else errorfct(5);
}